If you are using a basket-style air fryer (6-quart size), use an 8-inch round metal cake pan, stir all of the walnuts, chocolate chips, and marshmallows into the batter (do not reserve any for topping), and increase the cooking time to 1 hour. skip the broiling step. the brownies will be fudgy on the inside with an extra-crispy top layer. If you are using a toaster oven–style air fryer, you can use an 8-inch round or square metal cake pan for more evenly baked brownies, or an 8-inch square Pyrex dish for a brownie with an extra-gooey center. If you like, you can line the bottom of the cake pan with a round of parchment for easier unmolding. For an even quicker treat, you can use a store-bought brownie mix for this recipe. Any 18- to 19-ounce boxed mix will work well—I like the classic Betty Crocker fudge brownie mix. substitute the boxed mix for the powdered sugar, flour, and cocoa powder.